The present invention generally relates to a method of treating polymeric materials, such as biomedical devices and contact lenses. In particular, the present invention is directed to a method of altering the hydrophobic or hydrophilic nature of the polymeric surface of a biomedical device by applying a single-dip polyionic solution to form a layer-by-layer-like coating thereon.
Many devices used in biomedical applications require that the bulk of the device have one property, while the surface of the device has another property. For example, contact lenses may have high oxygen permeability through the lens to maintain good corneal health. However, materials that exhibit exceptionally high oxygen permeability (e.g. polysiloxanes) are typically hydrophobic and will adhere to the eye. Thus, a contact lens generally has a core or bulk material that is highly oxygen permeable and hydrophobic, and a surface that has been treated or coated to increase hydrophilic properties, thereby allowing the lens to freely move on the eye without adhering excessive amounts of tear lipid and protein.
In order to modify the hydrophilic nature of a relatively hydrophobic contact lens material, a contact lens can be treated with a plasma treatment. For example, a high quality plasma treatment technique is disclosed in PCT Publication No. WO 96/31793 to Nicholson et al. Some plasma treatment processes, however, require a significant monetary investment in certain equipment. Moreover, plasma treatment requires that the lens be dry before exposure to the plasma. Thus, lenses that are wet from prior hydration or extraction processes must be dried, thereby imposing added costs of obtaining drying equipment, as well as added time in the overall lens production process. As a result, a number of methods of consistently and permanently altering the surface properties of polymeric biomaterials, such as contact lenses, have been developed. Some of these techniques include Langmuir-Blodgett deposition, controlled spin casting, chemisorptions, and vapor deposition. Useful examples of Langmuir-Blodgett layer systems are disclosed in U.S. Pat. Nos. 4,941,997; 4,973,429; and 5,068,318.
A more recent technique used for coating electronic devices is a layer-by-layer (xe2x80x9cLbLxe2x80x9d) polymer absorption process, which is described in xe2x80x9cInvestigation of New Self-Assembled Multilayer Thin Films Based on Alternately Adsorbed Layers of Polyelectrolytes and Functional Dye Moleculesxe2x80x9d by Dongsik Yoo, et al. (1996). The process described in this article involves alternatively dipping hydrophilic glass substrates in a polyelectrolyte solution (e.g., polycations such as polyallylamine or polyethyleneimine) and then in an oppositely charged dye solution to form electrically conducting thin films and light-emitting diodides (LEDs). After each dipping, the substrates are rinsed with acidic aqueous solutions. Both the dipping and rinsing solutions have a pH of 2.5 to 7. Prior to dipping, the surfaces of the glass substrates are treated in order to create a surface having an affinity for the polyelectrolyte.
Similar to the above process, two other processes are described by xe2x80x9cMolecular-Level Processing of Conjugated Polymersxe2x80x9d by Fou and Rubner and Ferreira and Rubner, respectively. These processes involve treating glass substrates that have hydrophilic, hydrophobic, negatively, or positively charged surfaces. The glass surfaces are treated for extended periods in hot acid baths and peroxide/ammonia baths to produce a hydrophilic surface. Hydrophobic surfaces are produced by gas-phase treatment in the presence of 1,1,1,3,3,3-hexamethyldisilazane for 36 hours. Charged surfaces are prepared by covalently anchoring charges onto the surface of the hydrophilic slides. For example, positively charged surfaces are made by further treating the hydrophilic surfaces in methanol, methanol/toluene, and pure toluene rinses, followed, by immersion in (N-2 aminoethyl-3-aminopropyl) trimethyloxysilane solution for 12 to 15 hours. This procedure produces glass slides with amine functionalities, which are positively charged at a low pH.
In addition to the above-described techniques, U.S. Pat. Nos. 5,518,767 and 5,536,573 to Rubner et al. describe methods of producing bilayers of p-type doped electrically conductive polycationic polymers and polyanions or water-soluble, non-ionic polymers on glass substrates. These patents describe extensive chemical pre-treatments of glass substrates that are similar to those described in the aforementioned articles.
The methods described above generally relate to layer-by-layer polyelectrolyte deposition. However, these methods require a complex and time-consuming pretreatment of the substrate to produce a surface having a highly charged, hydrophilic, or hydrophobic nature in order to bind the polycationic or polyanionic material to the glass substrate.
To reduce the complexity, costs, and time expended in the above-described processes, a layer-by-layer polyelectrolyte deposition technique was developed that could be effectively utilized to alter the surfaces of various materials, such as contact lenses. This technique is described in co-pending U.S. Patent Application entitled xe2x80x9cApparatus, Methods, and Compositions for Modifying Surface Characteristicsxe2x80x9d. In particular, a layer-by-layer technique is described that involves consecutively dipping a substrate into oppositely charged polyionic materials until a coating of a desired thickness is formed. Nevertheless, although this technique provides an effective polyelectrolyte deposition technique for biomaterials, such as contact lenses, a need for further improvement still remains. For example, with this layer-by-layer dipping process, a coating could require multiple dipping steps that take a substantial amount of time to apply. As a result, manufacturing costs can often be increased due to the amount of time and dipping required to sufficiently coat the substrate.
As such, a need currently exists for an improved method of coating a material, such as a contact lens, with polyelectrolyte (polyionic) layers. In particular, a need exists for an improved polyionic deposition technique that requires less time and dipping than the previously-described layer-by-layer deposition technique.
Accordingly, an object of the present invention is to provide an improved method of treating polymers, such as ophthalmic lenses, to alter surface properties.
It is another object of the present invention to provide an improved method of treating polymers with polyionic materials to alter the hydrophilic or hydrophobic nature of their surfaces.
Still another object of the present invention is to provide an improved method of coating a polymer substrate with a polyionic material to alter the surface properties of the substrate.
Yet another object of the present invention is to provide an improved method of coating a polymer substrate with a polyanionic and a polycationic material.
Another object of the present invention is to provide a method of coating a polymer substrate with layers of a polyanion and polycation in a relatively short period of time.
It is another object of the present invention to provide a method for applying layers of a polyanion and polycation to a substrate in a single dip.
These and other objects of the present invention are achieved by providing a method for applying a polyionic solution to a substrate material, such as a contact lens. The method of the present invention can, in most embodiments, apply successive layers of polyionic material onto the substrate with only a single dip of the substrate into the polyionic solution.
In accordance with the present invention, a polyionic solution is employed to coat the substrate. In general, the polyionic solution contains at least one polycationic material and at least one polyanionic material, although more than one of each polyionic material can be employed. In one embodiment, for example, the polyionic solution is a bicomponent solution containing a polycation and a polyanion.
Typically, a polycationic material of the present invention can include any material known in the art to have a plurality of positively charged groups along a polymer chain. For example, in one embodiment, the polycationic material includes poly(allyl amine hydrochloride). Likewise, a polyanionic material of the present invention can typically include any material known in the art to have a plurality of negatively charged groups along a polymer chain. For example, in one embodiment, the polyanionic material includes polyacrylic acid.
According to the present invention, a polycationic material is combined with a polyanionic material to form the polyionic solution. In general, the polyionic components are added in non-stoichiometric amounts such that one of the components is present within the solution in a greater amount than another component. In particular, the molar charge ratio, as defined herein, can be from about 3:1 to about 100:1. In certain embodiments, the molar charge ratio is 10:1 (polyanion:polycation).
By increasing the molar charge ratio, a polyionic solution of the present invention can be xe2x80x9cself-cascadedxe2x80x9d onto a substrate. In other words, when the substrate is dipped into the solution, alternating layers of polyionic components can be coated onto the substrate. For example, in one embodiment, polyanionic-polycationic-polyanionic alternating repeating layers are assembled when the substrate is dipped into the solution.
Besides containing polyionic components, a polyionic solution of the present invention can also contain various other materials. For example, the polyionic solution can contain antimicrobials, antibacterials, radiation-absorbing materials, cell growth inhibitors, etc.
In accordance with the present invention, it is typically desired to maintain the pH of the solution within a certain range. Maintenance of pH can help prevent precipitation of one of the polyionic components from solution. Accordingly, in one embodiment, the pH is maintained within about xc2x10.5 of an appropriate pH. Preferably, the pH is maintained within about xc2x10.1 of an appropriate pH. In general, the appropriate pH for a given solution is at least partially dependent on the polyionic materials selected and can be determined by any suitable method known in the art.
As noted above, after forming the polyionic solution according to the present invention, a substrate material is generally dipped into the solution such that it becomes sufficiently coated. In general, a substrate material of the present invention can be made from any polymeric material. In particular, a substrate material of the present invention can be made from oxygen-permeable polymeric materials. For example, some examples of suitable substrate materials, include, but are not limited to, the polymeric materials disclosed in U.S. Pat. No. 5,760,100 to Nicolson et al., which is incorporated herein by reference.
In some embodiments, the substrate can also be xe2x80x9cpreconditionedxe2x80x9d to enhance the ability of the polyionic solution to coat the substrate. In one embodiment, for example, a layer-by-layer application process can be used to form an underlayer or primer coating on the substrate. This underlayer can sufficiently xe2x80x9croughenxe2x80x9d the surface such that the ultimate single-dip coating solution of the present invention can better adhere to the substrate surface.
Moreover, in another embodiment, a solvent solution can be initially applied to the substrate for preconditioning. The application of a solvent, such as an alcohol solution, in the presence of a polyionic component or multiple polyionic components, can allow the substrate to swell. After swelling, the substrate can then be removed from the solvent solution and then dipped into a polyionic solution so that it shrinks. The shrinking of the substrate can entrap the polyionic component(s) within the substrate. As a result, in some embodiments, the ultimate single-dip solution of the present invention more easily adheres to the substrate surface when applied thereto.
In contrast to the heretofore-mentioned layer-by-layer processes, a process of the present invention can apply alternating layers of a polyionic solution to a substrate with only a single dip, thus saving a substantial amount of time. For example, coatings of from about 40 angstroms to about 1000 angstroms can be applied in a single dip. Morever, the time for applying such coating can be less than 6 minutes and even as little as 1 minute.
Other objects, features and aspects of the present invention are discussed in greater detail below.
Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present invention are disclosed in or are obvious from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.
In general, the present invention is directed to an improved method of coating substrate materials, such as contact lenses, with a solution of negatively and positively charged materials, such as polyionic materials. In particular, the present invention is directed to a process employing a coating solution that includes both a polycation and polyanion maintained at a certain pH level. It has been discovered that a process of the present invention can sufficiently coat a substrate material with a certain thickness of polyionic layers in a substantially less time period than prior coating processes. For example, in one embodiment, a single dip process of the present invention can be employed to provide a 100 angstrom thick coating in about 6 minutes.
In accordance with the present invention, a coating process is provided that can be utilized to deposit polyionic materials onto a substrate. In one embodiment, for example, a process of the present invention allows the deposition of a bicomponent polyionic solution to a biomaterial substrate, such as a contact lens.
To form a coated substrate of the present invention, a coating solution is initially formed. As stated, a coating solution of the present invention can include polyionic materials, such as polyanionic or polycationic materials. Examples of such polyionic materials are disclosed in U.S. patent application Ser. No. 09/199,609 filed on Nov. 25, 1998, which is incorporated herein by reference and discussed below. For instance, a first material may be a polycationic material, which can include any material known in the art to have a plurality of positively charged groups along a polymer chain. Such materials can include, but are not limited to:
(a) poly(allylamine hydrochloride) (PAH) 
(b) poly(ethyleneimine) (PEI) 
(c) poly(vinylbenzyltriamethylamine) (PVBT) 
(d) polyaniline (PAN or PANI) (p-type doped) [or sulphonated polyaniline]
(e) polypyrrole (PPY) (p-typed doped) 
(f) poly(pyridinium acetylene) 
Moreover, a second material may be a polyanionic material, which can generally include any material known in the art to have a plurality of negatively charged groups along a polymer chain. For example, suitable anionic materials can include, but are not limited to:
(a) polymethacrylic acid (PMA) 
(b) polyacrylic acid (PAA) 
(c) poly(thiophene-3-acetic acid) (PTAA) 
(d) poly(4-styrenesulfonic acid) (PSS) or sodium poly(styrene sulfonate) (SPS) or poly(sodium styrene sulfonate) (PSSS) 
In certain embodiments, either the polyanionic or polycationic material can be made from derivatives of a polyallyl amine having a weight average molecular weight of at least 2000 that, based on the number of amino groups of the polyallyl amine, comprises from approximately 1 to 99% of units having the following formula (1): 
wherein M is a xe2x80x9cmodifier unitxe2x80x9d. For instance, in one embodiment, the modifier unit, M, can be Rxe2x80x94Cxe2x95x90O, where R is C2-C6 alkyl that is substituted by two or more same or different substituents selected from the group consisting of hydroxy, C2-C5 alkanoyloxy, and C2-C5 alkylamino carbonyloxy. Preferably, R is linear C3-C6 alkyl, more preferably linear C4-C5 alkyl, and most preferably n-pentyl that is in each case substituted as defined above.
Suitable substituents of the alkyl radical R are xe2x80x94OH, a radical xe2x80x94Oxe2x80x94C(O)xe2x80x94R1, and/or a radical xe2x80x94Oxe2x80x94C(O)xe2x80x94NHxe2x80x94R1xe2x80x2, wherein R1 and R1xe2x80x2 are each independently of the other C1-C4 alkyl, preferably methyl, ethyl, iso-, or n-propyl, and more preferably methyl or ethyl. Preferred substituents of the alkyl radical R are hydroxy, acetyloxy, propionyloxy, iso- or n-butanoyloxy, methylaminocarbonyloxy or ethylaminocarbonyloxy, especially hydroxy, acetyloxy, or propionyloxy, and in particular hydroxy.
A particular embodiment of the present invention relates to units of formula (1), wherein R is linear Cp-alkyl comprising xe2x80x9cpxe2x80x9d same or different above-mentioned substituents, and wherein p is 2, 3, 4, 5, or 6, and preferably 4 or 5, and more preferably 5. Alternatively, R may be Cp-alkyl comprising xe2x80x9cpxe2x80x9d hydroxy groups that may be partly or completely acetylated, wherein p is 4 or 5, and preferably 6. Particular radicals R are 1,2,3,4,5-pentahydroxy-n-pentyl or 1,2,3,4,5-pentahydroxy-n-pentyl, wherein the hydroxy groups are partly or completely acetylated.
As stated above, embodiments of a polyionic material of the present invention include derivatives of a polyallyl amine that, based on the number of amino groups of the polyallyl amine, comprise from about 1 to about 99%, in some embodiments from about 10 to about 80%, in some embodiments from about 15 to about 75%, and in other embodiments from about 40 to about 60%, of units of formula (1). In general, polyionic materials of the present invention are also water-soluble.
A particular group of polyallyl amine polymers useful in the present invention comprise at least 1%, in some cases at least 5%, and in other cases at least 10% of units of PAH, based on the number of amino groups of the polyallyl amine. Moreover, one group of polyallyl amine polymers may have a weight average molecular weight of, for example, from 2,000 to 1,000,000, from 3,000 to 500,000, from 5,000 to 150,000, or more particularly from 7,500 to 100,000.
The polyallyl amine polymers described above may be prepared by any manner known in the art. For example, a polyallyl amine having a weight average molecular weight of at least 2,000 that comprises units of PAH may be reacted with a lactone having the following formula (6): 
wherein (alk) is linear or branched C2-C6-alkylene, the sum of (t1-t2-t3) is at least 1, and R1 and R1xe2x80x2 as defined above, to yield a polyallyl amine polymer comprising units of formula (1) and PAH.
The reaction between the polyallyl amine and the lactone may be performed in any manner known in the art, such as, by reacting the polyallyl amine with the lactone in an aqueous medium at a temperature from about 20xc2x0 C. to about 100xc2x0 C., and, in some cases, from 30xc2x0 C. to 60xc2x0 C. The ratio of units of formula (1) and formula PAH in the final polymer is determined by the stoichiometry of the reactants. The lactones of formula (6) are known or may be prepared according to known methods. Compounds of formula (6), wherein t2 or t3xe2x89xa71 are, for example, available by reacting the respective hydroxy compound of formula (6) with a compound R1xe2x80x94C(O)X or R1xe2x80x2xe2x80x94NCO under conditions well known in the art. Polyallyl amine starting materials of different molecular weights are commercially available, e.g. in the form of the hydrochloride. Hydrochloride can be converted previously into the free amine, for example, by a treatment with a base, such as sodium or potassium hydroxide solution.
Polyallyl amines comprising additional xe2x80x9cmodifier unitsxe2x80x9d, M, may be prepared by adding to the reaction a mixture of the polyallyl amine and the compound of formula (6), simultaneously or preferably successively. Some examples of compounds that can be added to a polyallyl amine and the compound of formula (6) include, but are not limited to, the following: 
wherein X is halogen, preferably chlorine; (alkxe2x80x2) is C1-C12-alkylene; R12 is hydrogen or C1-C2-alkyl, preferably hydrogen or methyl; and R3, R4, R5xe2x80x2, R6 and Q1 are as defined above. The reaction proceeds, for example, in an aqueous solution at room temperature or at an elevated temperature, such as from 25xc2x0 C. to about 60xc2x0 C. and yields various polymers comprising various modifier units.
Because the reaction of the amino groups of the polyallyl amine with the compounds of formulae (6) or (6a)-(6k) proceeds, in general, quantitatively, the structure of the modified polymers is determined mainly by the stoichiometry of the reactants that are employed into the reaction. A particular polyionic material is polyallylamine gluconolactone, as shown below in formula (7): 
The polyallyl amine may be one in which about 20% to about 80% of the amino groups have been reacted with delta-glucolactone to yield R groups of formula (7).
In order to alter various characteristics of the coating, such as thickness, the molecular weight of the polyionic materials can be varied. In particular, as the molecular weight is increased, the coating thickness generally increases. However, if the increase in molecular weight increase is too substantial, the difficulty in handling may also increase. As such, polyionic materials used in a process of the present invention will typically have a molecular weight Mn of about 10,000 to about 150,000. In certain embodiments, the molecular weight is about 25,000 to about 100,000, and in other embodiments from about 75,000 to about 100,000.
In addition to polyionic materials, a coating solution of the present invention can also contain additives. As used herein, an additive can generally include any chemical or material. For example, active agents, such as antimicrobials and/or antibacterials can be added to a coating solution of the present invention, particularly when used in biomedical applications. Some antimicrobial polyionic materials include polyquaternary ammonium compounds, such as those described in U.S. Pat. No. 3,931,319 to Green et al. (e.g. POLYQUAD(copyright)), which is incorporated herein by reference.
Moreover, others examples of materials that can be added to a coating solution of the present invention are polyionic materials useful for ophthalmic lenses, such as materials having radiation absorbing properties. Such materials can include, for example, visibility tinting agents, iris color modifying dyes, and ultraviolet (UV) light tinting dyes. Still another example of a material that can be added to a coating solution of the present invention is a polyionic material that inhibits or induces cell growth. Cell growth inhibitors can be useful in devices that are exposed to human tissue for an extended time with an ultimate intention to remove (e.g. catheters), while cell growth-inducing polyionic materials can be useful in permanent implant devices (e.g. artificial cornea).
When additives are applied to a coating solution of the present invention, it is generally desired that the additives have some charge. By having a positive or negative charge, the additive can be substituted for one of the polyionic materials in solution at the same molar charge ratio. For example, polyquaternary ammonium compounds typically have a positive charge. As such, these compounds can be substituted into a solution of the present invention for the polycationic component such that the additive is applied to a substrate material in a manner similar to how a polycationic would be applied.
It should be understood, however, that non-charged additives can also be applied to a substrate material of the present invention. For example, in one embodiment, a polycationic layer can be first applied onto a substrate material. Thereafter, a non-charged additive can be applied and immediately entrapped by a polyanionic material applied thereon. In this embodiment, polyanionic material can sufficiently entrap the non-charged additive between two layers of polyionic material. After such entrapment, the substrate material can then be coated with other layers of polyionic materials in accordance with the present invention.
As discussed above, a coating solution of the present invention can generally be formed from polyionic materials and various other chemicals. In one embodiment, a coating solution of the present invention can be a bicomponent solution that contains at least one polycationic and polyionic material. In other embodiments, the coating solution can contain more than two components of a polyionic materials, such as 3, 4, or 5 components.
Regardless of the number of polyionic components present within a coating solution of the present invention, it is typically desired that one of the polyionic components of the solution be present in a greater amount than another component such that a non-stoichiometric solution can be formed. For example, when a polyanionic/polycationic bicomponent solution is formed, either one of the polyionic components can be present in an amount greater than the other component. By forming a solution from polyionic materials in such a manner, a substrate material can be suitably coated with the coating solution in a single dip. Specifically, the non-stoichiometric concentrations of polyionic materials provides a solution that can xe2x80x9cself-cascadexe2x80x9d such that alternating layers of polyionic materials are formed onto the substrate with a single dip.
To control the amount of each polyionic component within a coating solution, the xe2x80x9cmolar charge ratioxe2x80x9d can be varied. As used herein, xe2x80x9cmolar charge ratioxe2x80x9d is defined as the ratio of charged molecules in solution on a molar basis. For example, a 10:1 molar charge ratio can be defined as 10 molecules of a polyanion to 1 molecule of a polycation, or 10 molecules of a polycation to 1 molecule of a polyanion. The molar charge ratio can be determined as defined above for any number of components within a solution, as long as at least one polycation and one polyanion are included therein.
As the molar charge ratio is substantially increased, the structure of the coating on a particular substrate can become more xe2x80x9copenxe2x80x9d. In some instances, such an opening of the coating structure can result in the requirement of more dipping steps to achieve the desired coating on the substrate material. In this regard, a coating solution of the present invention typically has a xe2x80x9cmolar charge ratioxe2x80x9d from about 3:1 to about 100:1. In one embodiment, the coating solution has a molar charge ratio of about 5:1 (polyanion:polycation). In another embodiment, the coating solution has a molar charge ratio of about 1:5 (polyanion:polycation). In still another embodiment, a 3:1 or 1:3 molar charge ratio may be utilized.
In a certain embodiment, the coating solution has a molar charge ratio of about 10:1 (polyanion:polycation). By employing a coating solution having a predominant amount of polyanionic material, a substrate material can be coated in a manner such that the outer layer is a polyanionic material. Substrates having an outer polyanionic material are typically more acidic. It is believed that in some applications, an acidic outer layer can provide a more hydrophilic substrate and allow better wetting. However, it should be understood that an outer layer of polycationic material may also be desirable. In contrast to a polyanionic outer coating, a polycationic outer coating can be achieved by providing a coating solution that contains a predominant amount of polycationic material.
In accordance with the present invention, a coating solution of the present invention is typically maintained at a certain pH level such that the solution remains stable. When the pH of the coating solution is improperly varied, a salt can sometimes form through back-titration. Such precipitation can often have an adverse affect on the ability of the coating solution to coat the substrate layer as desired. As such, depending on the particular coating solution used, the pH of the solution is normally maintained at a value within about xc2x10.5 of the appropriate pH range for the solution. In certain embodiments, the pH of the coating solution is maintained at a pH of xc2x10.1 of the appropriate pH range for the solution. By maintaining the pH of the solution within a specified range of the appropriate pH for the solution, precipitation can be substantially inhibited.
The appropriate pH range for a coating solution can vary depending on the particular polyionic materials chosen. Any suitable method known in the art can be utilized to determine the appropriate pH range for a given solution. One such method is described in xe2x80x9cControlling Bilayer Composition and Surface Wettability of Sequentially Adsorbed Multilayers of Weak Polyelectrolytesxe2x80x9d by Dougsik Yoo, Seimel S. Shiratori, and Michael R. Rubner, which is published in MACROMOLECULES(copyright) Volume 31, Number 13, pages 4309-4318 (1998). For example, in a particular embodiment, a 10:1 (polyanion:polycation) ratio of polyacrylic acid and polyallylamine hydrochloride is utilized. For this particular bicomponent coating solution, the appropriate pH range was determined to be about 2.5.
In accordance with the present invention, a coating solution of the present invention, as described above, can be prepared in a variety of ways. In particular, a coating solution of the present invention can be formed by dissolving the polyionic materials in water or any other material that sufficiently dissolves the material. When a solvent is used, any solvent that can allow the components within the coating solution to remain stable in water is suitable. For example, an alcohol-based solvent can be used. Suitable alcohols can include, but are not limited to, isopropyl alcohol, hexanol, ethanol, etc. It should be understood that other solvents commonly used in the art can also be suitably used in the present invention.
Whether dissolved in water or in a solvent, the concentration of the polyionic materials within a coating solution of the present invention can generally vary depending on the particular materials being utilized, the desired coating thickness, and a number of other factors. However, it may be typical to formulate a relatively dilute aqueous solution of polyionic material. For example, a polyionic material concentration can be between about 0.001% to about 0.25% by weight, between about 0.005% to about 0.10% by weight, or between about 0.01% to about 0.05% by weight.
In this regard, one embodiment a bicomponent coating solution of the present invention can be prepared as follows. However, it should be understood that the following description is for exemplary purposes only and that a coating solution of the present invention can be prepared by other suitable methods.
A bicomponent coating solution can be prepared by first dissolving a single component polyanionic material in water or other solvent at a designated concentration. For example, in one embodiment, a solution of polyacrylic acid having a molecular weight of about 90,000 is prepared by dissolving a suitable amount of the material in water to form a 0.001M PAA solution. Once dissolved, the pH of the polyanionic solution can be properly adjusted by adding a basic or acid material. In the embodiment above, for example, a suitable amount of 1N hydrochloric acid (HCl) can be added to adjust the pH to 2.5.
After preparing the polyanionic solution, the polycationic solution can be similarly formed. For example, in one embodiment, poly(allylamine hydrochloride) having a molecular weight of about 50,000 to about 65,000 can be dissolved in water to form a 0.001M solution. Thereafter, the pH can be similarly adjusted to 2.5 by adding a suitable amount of hydrochloric acid.
The formed solutions can then be mixed to form a single-dip coating solution of the present invention. In one embodiment, for example, the solutions above can be mixed slowly to form the coating solution. The amount of each solution applied to the mix depends on the molar charge ratio desired. For example, if a 10:1 (polyanion:polycation) solution is desired, 1 part (by volume) of the PAH solution can be mixed into 10 parts of the PAA solution. After mixing, the solution can also be filtered if desired.
Once a coating solution is formed in accordance with the present invention, it can then be applied to a substrate material. In one embodiment, a coating solution of the present invention can also be applied to a mold for forming a polymeric material, such as disclosed in co-pending U.S. patent application entitled xe2x80x9cMethod for Modifying a Surfacexe2x80x9d (filed on the same day as present application), which is incorporated herein by reference. Thus, although the embodiment discussed below relates to the direct application of a coating solution to the substrate material, other methods of coating the substrate are equally suitable.
Thus, to coat a substrate material, it can be dipped into a coating solution such that the substrate becomes sufficiently coated with the polyionic materials. The coating solution contains both a polyanion and polycation within a single solvent such that a single dip can result in alternating layers of polyionic material. For example, a single dip of a substrate material can result in the substrate being coated with cascaded layers of polyanion-polycation-polyanion-polycation, etc.
In general, a substrate material dipped into a coating solution can be made from any polymeric material, such as contact lenses, molds for forming contact lenses, or shaped polymeric materials. When forming a contact lens, the substrate material may be an oxygen-permeable material, such as flourine- or siloxane- containing polymers. For example, the polymeric materials described in U.S. Pat. No. 5,760,100 to Nicolson et al., are suitable substrate materials for use in the present invention. For illustrative purposes, other examples of suitable materials are disclosed below, without limitation.
One embodiment of a suitable substrate material of the present invention is a copolymer formed from the following monomeric and macromeric components:
(a) about 5 to about 94 dry weight percent of a macromer having the segment of the formula:
CP-PAO-DU-ALK-PDMS-ALK-DU-PAO-CP
where
PDMS is a divalent poly(disubstituted siloxane),
ALK is an alkylene or alkylenoxy group having at least 3 carbon atoms,
DU is a diurethane-containing group,
PAO is a divalent polyoxyalkylene, and
CP is selected from acrylates and methacrylates,
wherein said macromer has a number-average molecular weight of about 2000 to about 10,000;
(b) about 5 to about 60 weight percent methacryloxypropyltris (trimethylsiloxy)silane;
(c) about 1 to about 30 weight percent of an acrylate or methacrylate monomer; and
(d) 0 to about 5 weight percent cross-linking agent, with the weight percentages being based upon the dry weight of the polymer components.
Moreover, a particular polysiloxane macromer segment is defined by the formula:
xe2x80x83CP-PAO-DU-ALK-PDMS-ALK-DU-PAO-CP
where
PDMS is a divalent poly(disubstituted siloxane);
CP is an isocyanatoalkyl acrylate or methacrylate, preferably isocyanatoethyl methacrylate, where the urethane group is bonded to the terminal carbon on the PAO group;
PAO is a divalent polyoxyalkylene (which may be substituted), and is preferably a polyethylene oxide, i.e., (xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94)mCH2xe2x80x94CH2xe2x80x94 where m may range from about 3 to about 44, more preferably about 4 to about 24;
DU is a diurethane (which may be a cyclic structure),
where an oxygen of the first urethane linkage is bonded to the PAO group and an oxygen of the second urethane linkage is bonded to the ALK group;
and ALK is an alkylene or alkylenoxy group having at least 3 carbon atoms, such as a branched alkylene group or an alkylenoxy group having 3 to 6 carbon atoms, such as a sec-butyl (i.e., xe2x80x94CH2CH2CH(CH3)xe2x80x94) group or an ethoxypropoxy group (e.g., xe2x80x94Oxe2x80x94(CH2)2xe2x80x94Oxe2x80x94(CH2)3xe2x80x94).
Another embodiment of a suitable substrate material of the present invention is a macromer having the following general formula I:
P1xe2x80x94(Y)mxe2x80x94(Lxe2x80x94X1)pxe2x80x94Qxe2x80x94(X1xe2x80x94L)pxe2x80x94(Y)mxe2x80x94P1
where each P1, independently of the others, is a free radical-polymerizable group;
each Y, independently of the others, is xe2x80x94CONHCOOxe2x80x94, xe2x80x94CONHCONHxe2x80x94, xe2x80x94OCONHCOxe2x80x94, xe2x80x94NHCONHCOxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94NHCONHxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94NHCOOxe2x80x94or xe2x80x94OCONHxe2x80x94;
m and p, independently of one another, are 0 or 1;
each L, independently of the others, is a divalent radical of an organic compound having up to 20 carbon atoms;
each X1, independently of the others, is xe2x80x94NHCOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94
NHCONHxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94NHCOOxe2x80x94or xe2x80x94OCONHxe2x80x94; and
Q is a bivalent polymer fragment consisting of the segments:
(a) xe2x80x94(E)kxe2x80x94Zxe2x80x94CF2xe2x80x94(OCF2)xxe2x80x94(OCF2CF2)yxe2x80x94OCF2xe2x80x94Zxe2x80x94(E)kxe2x80x94,
where x+y is a number in the range of about 10 to about 30;
each Z, independently of the others, is a divalent radical having up to about 12 carbon atoms or Z is a bond;
each E, independently of the others, is xe2x80x94(OCH2CH2)qxe2x80x94, where q has a value of from 0 to about 2, and where the link xe2x80x94Zxe2x80x94Exe2x80x94represents the sequence xe2x80x94Zxe2x80x94(OCH2CH2)qxe2x80x94; and
k is 0 or 1; 
where n is an integer from about 5 to about 100;
Alk is alkylene having up to about 20 carbon atoms;
about 80% to about 100% of the radicals R1, R2, R3 and R4, independently of one another, are alkyl and 0 to about 20% of the radicals R1, R2, R3 and R4, independently of one another, are alkenyl, aryl or cyanolkyl; and
(c) X2xe2x80x94Rxe2x80x94X2,
where R is a divalent organic radical having up to 20 carbon atoms; and
each X2, independently of the others, is xe2x80x94NHCOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94NHCONHxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94NHCOOxe2x80x94, or OCONHxe2x80x94;
with the provisos that there is typically at least one of each segment (a), (b), and (c) in Q, that each segment (a) or (b) has a segment (c) attached to it, and that each segment (c) has a segment (a) or (b) attached to it.
The number of segments (b) in the polymer fragment may be greater than or equal to the number of segments (a). The ratio between the number of segment (a) and (b) in the polymer fragment Q, for example, may be about 3:4, 2:3, 1:2 or 1:1. The molar ratio between the number of segments (a) and (b) in the polymer fragment Q may be, for example, 2:3, 1:2 or 1:1.
The mean molecular weight of the polymer fragment Q is in the range of about 1,000 to about 20,000, sometimes in the range of about 3000 to about 15,000, and sometimes in the range of about 5,000 to about 12,000.
The total number of segments (a) and (b) in the polymer fragment Q may be in the range of about 2 to about 11, in the range of about 2 to about 9, or in the range of about 2 to about 7. The smallest polymer unit Q may be composed of one perfluoro segment (a), one siloxane segment (b) and one segment (c).
In still another embodiment of the present invention, the substrate material can be formed by polymerizing macromers that contain free hydroxyl groups. Macromers that are built up, for example, from an amino-alkylated polysiloxane derivatized with at least one polyol component that contains an unsaturated polymerizable side chain may be utilized. In one embodiment, polymers can be prepared from the macromers according to the invention by homopolymerization. The macromers mentioned can also be mixed and polymerized with one or more hydrophilic and/or hydrophobic comonomers. A special property of the macromers according to the invention is that they function as the element which controls microphase separation between selected hydrophilic and hydrophobic components in a cross-linked end product. The hydrophilic/hydrophobic microphase separation is in the region of less than about 300 nm. The macromers may be cross-linked at the phase boundaries between, for example, an acrylate comonomer on the one hand and an unsaturated polymerizable side chain of polyols bonded to polysiloxane by covalent bonds, and additionally by reversible physical interactions such as hydrogen bridges. These are formed, for example, by numerous amide or urethane groups. The continuous siloxane phase that exists in the phase composite has the effect of producing a high permeability to oxygen.
The polymers of this embodiment can be formed by polymerizing a macromer comprising at least one segment having the following general formula (II): 
in which,
(a) is a polysiloxane segment,
(b) is a polyol segment which contains at least 4 carbon atoms,
Z is a segment (c) or a group X1, and
(c) is defined as X2xe2x80x94Rxe2x80x94X2, wherein
R is a bivalent radical of an organic compound having up to 20 carbon atoms and
each X2 independently of the other is a bivalent radical which contains at least one carbonyl group,
X1 is defined as X2, and
(d) is a radical having the following general formula (III):
X3xe2x80x94Lxe2x80x94(Y)kxe2x80x94P1
in which,
P1 is a group that can be polymerized by free radicals;
Y and X3 independently of one another are a bivalent radical which contains at least one carbonyl group;
k is 0 or 1; and
L is a bond or a divalent radical having up to 20 carbon atoms of an organic compound.
In one embodiment, a polysiloxane segment (a) can be derived from a compound having the following general formula (IV): 
in which,
n is an integer from 5 to 500;
25%-99.8% of the radicals R1, R2, R3, R4, R5, and R6 independently of one another are alkyl and 0.2%-75% of the radicals R1, R2, R3, R4, R5, and R6 independently of one another are partly fluorinated alkyl, aminoalkyl, alkenyl, aryl, cyanoalkyl, alkxe2x80x94NHxe2x80x94alkxe2x80x94NH2 or alkxe2x80x94(OCH2)mxe2x80x94(OCH2)pxe2x80x94OR7,
where R7 is hydrogen or lower alkyl, alk is alkylene, and
m and p independently of one another are an integer from 0 to 10, one molecule containing at least one primary amino or hydroxyl group.
The alkylenoxy groups xe2x80x94(OCH2CH2)m and xe2x80x94(OCH2)p in the siloxane of the formula (IV) are either distributed randomly in a ligand alkxe2x80x94(OCH2CH2)mxe2x80x94(OCH2)pxe2x80x94OR7 or are distributed as blocks in a chain.
A polysiloxane segment (a) is linked a total of about 1 to about 50 times, and, for example, about 2 to about 30 times, and in particular about 4 to about 10 times, via a group Z with a segment (b) or another segment (a), Z in an a-Z-a sequence typically being a segment (c). The linkage site in a segment (a) with a group Z is an amino or hydroxyl group reduced by one hydrogen.
Another embodiment of a substrate material of the present invention involves the polymerization of a siloxane-containing macromer formed from a poly(dialkylsiloxane) dialkoxyalkanol having the following structure (V): 
where n is an integer from about 5 to about 500, preferably about 20 to about 200, more preferably about 20 to about 100;
the radicals R1, R2, R3, and R4, independently of one another, are lower alkylene, for example a C1-C6 alkylene, C1-C3 alkylene, and wherein, in some embodiments, the total number of carbon atoms in R1 and R2 or in R3 and R4 is greater than 4; and
R5, R6, R7, and R8 are, independently of one another, lower alkyl, in some embodiments, a C1-C6 alkyl, and in some embodiments, a C1-C3 alkyl.
The general structure of the macromer discussed above is as follows:
ACRYLATE-LINK-ALK-O-ALK-PDAS-ALK-O-ALK-LINK-ACRYLATE
where the ACRYLATE is selected from acrylates and methacrylates; LINK is selected from urethanes and dirurethane linkages, ALK-O-ALK is, as defined above, (R1xe2x80x94Oxe2x80x94R2 or R3xe2x80x94Oxe2x80x94R4), and PDAS is a poly(dialkylsiloxane).
For example, the macromer described above can be prepared by reacting isophorone diisocyanate, 2-hydroxyethyl (meth)acrylate and a poly(dialkylsiloxane) dialkoxyalkanol in the presence of a catalyst.
In some embodiments of the present invention, the particular substrate material utilized can also be xe2x80x9cpre-conditionedxe2x80x9d or xe2x80x9corientedxe2x80x9d before being dipped into a coating solution. Although not required, pre-conditioning the substrate material in accordance with the present invention can enhance the xe2x80x9cself cascadingxe2x80x9d of polyionic layers in a single dip process. In particular, pre-conditioning a substrate material typically involves increasing the roughness of the substrate surface.
In this regard, the roughness of the substrate surface can be altered in a variety of ways. Generally, an xe2x80x9cunderlayerxe2x80x9d or xe2x80x9cprimer layerxe2x80x9d of coating solution can be initially applied to the substrate material to accomplish the desired surface alteration. For example, in one embodiment, one or more standard layer-by-layer dip coatings can be employed as an underlayer for the ultimate dip coating of the present invention. The xe2x80x9cunderlayerxe2x80x9d can be applied by any method known in the art, such as by spray-coating, dipping, etc. Examples of such methods are disclosed in detail in co-pending U.S. application Ser. No. 09/199,609. In some embodiments, the underlayer can be made from a polyionic material, such as poly(ethyleneimine). After applying this primer coating or underlayer, in one embodiment, the substrate can then be dipped into the ultimate coating solution. For instance, in one embodiment, the ultimate coating solution can contain poly(allylamine hydrochloride) and polyacrylic acid. In still another embodiment, the coating solution can contain poly(allylamine hydrochloride) and sodium poly(styrene sulfonate).
Moreover, in another embodiment, the substrate material can be allowed to swell in a solvent solution containing a solvent and at least one polyionic component(s). In general, any solvent that can allow the components within the coating solution to remain stable in water is suitable for use in the present invention. Examples of suitable alcohols can include, but are not limited to, isopropyl alcohol, hexanol, ethanol, etc. In certain embodiments, the substrate material is first allowed to swell in an alcohol solution containing about 20% isopropyl alcohol and about 80% water. In some embodiments, the alcohol solution used to swell the substrate can also be used as the solvent in the ultimate single-dip polyionic coating solution.
After swelling, the substrate material can then be removed from the solvent solution and allowed to xe2x80x9cshrinkxe2x80x9d. This xe2x80x9cshrinkingxe2x80x9d step causes the substrate material to entrap the initial layer of the polycation or polyanion present within the solvent solution. The swelling/entrapment process described in this embodiment can enhance the ability of the coating solution to coat the substrate material.
It has been discovered that, in most cases, a process of the present invention can apply a coating solution to a substrate material with only a single dip. As such, in contrast to the aforementioned LbL process, a process of the present invention can apply a coating in relatively little time. For example, coatings can be applied in a time period as little as one minute. Moreover, in some applications, a 100 angstrom coating can be applied in about 6 minutes using a single dip, whereas a similar coating could take approximately 10 hours to apply using the aforementioned LbL process (e.g. 20 dips). Moreover, it has been discovered that, in certain applications, a process of the present invention can apply coatings from about 40 angstroms to about 2000 angstroms in a single dip.
However, it may often be desired to apply a coating having a substantial thickness that cannot be sufficiently applied with a single dip. For example, in one embodiment of the present invention, a 500 angstrom coating is applied to a substrate material in two dipping steps. In particular, a 10:1 polyanion to polycation dip is first applied to the substrate material. Thereafter, a 1:10 polyanion to polycation is employed as a second coating layer. In some embodiments, more than two dips, such as 3 to 5 dips in multi-component solutions of the present invention can be utilized. For example, when coating a contact lens material according to the present invention, three dips may be utilized. However, even when more than one dipping step is utilized with solutions of the present invention, the substrate material can still be coated in substantially less time than with a LbL process. In fact, a LbL process could take approximately 50 hours (e.g. 100 dips) to apply a 500 angstrom coating, while a process of the present inventive single dip process can take approximately 8 to 30 minutes (e.g. 4 or 5 dips) to achieve the same thickness.
In one embodiment of the present invention, the single-dip solution can also be utilized for coating of a mold used to define the shape of an article. Coating a mold in this manner can prove useful in processes such as transfer grafting a polyionic coating. An example of such a process is disclosed in more detail with a co-pending U.S. Patent Application entitled xe2x80x9cMethod of Modifying a Surfacexe2x80x9d (filed on the same day as the present application). In one embodiment, the mold is coated with a polyionic solution of the present invention, but at least a portion of the coating is transferred from the mold when the liquid molding material (e.g., polymerizable material) is dispensed into the mold for formation of the solid article. Hence, another embodiment of the invention is a method of forming an article and coating the article by transfer grafting a coating material from the mold in which the article was produced. This method includes the steps of applying a coating of a polyionic solution to a mold by contacting at least a portion of the mold with the solution, dispensing a liquid molding material into the mold, thereby contacting said liquid molding material with said coating, allowing the mold coating to contact the liquid molding material during curing and causing the liquid mold material to harden (e.g., by polymerization via application of UV light). As a result, the coating can remain in tact and xe2x80x9ctransferxe2x80x9d to the solidified article.